The invention is related to a driving apparatus and, more particularly to a device driving fan motors.
Referring to FIG. 1, a controller 2 is utilized to drive a fan motor 1. As shown in FIG. 1, the controller 2, such as an integrated circuit (IC), has a plurality of pins for connection to some electrical devices such as a hall sensor 3, temperature sensor 4, and converter 5. The hall sensor 3 extracts a phase wave signal from the fan motor 1 and delivers the phase wave signal to the controller 2. The temperature sensor 4 can detect temperature and generate a voltage signal to the controller 2 by using a thermal resistor 41. The converter 5 converts an external pulse width modulation (PWM) signal to a voltage signal so as to input to the controller 2.
The controller 2 generates a driving signal to drive the fan motor 1 after receiving the voltage signals from the converter 5 and the temperature sensor 4. Referring to FIG. 2, a chart illustrates the relationships of the rotation speeds corresponding to various duty cycles of a PWM signal in different temperature. It is very clear to show that the lines in FIG. 2 are linear. When PWM signals with duty cycle are provided from 0% to 100% at any particular fixed temperature, the corresponding output rotation speeds follow a linear scale. In most applications, however, the rotation speed is not required to be linear to the duty cycle of the PWM signal. In fact, in applications such as large scale computers, if the rotation speeds of a system fan increase as the duty cycle of the PWM signal increases when the system is switched on or in standby mode, the resulting noise is bothersome.